1. Field of the Invention
The present invention relates to an optical recording film and a process for the production thereof, and further to a film for optical recording, a process for the production thereof and a composition useful for the production of the film for optical recording.
2. Prior Art
Holograms are known which are classified into amplitude and phase types (refractive index modulation types) in respect of their recording principles, into surface and volume types in respect of their structures, and into transmission (opposing direction) and reflection (same direction) types in respect of directions of illuminating light and diffracted light in reconstruction. Among these, a volume phase type is excellent particularly in optical characteristics such as diffraction efficiency. It has been already demonstrated that the maximum diffraction efficiency of the volume phase type including the transmission type and the reflection type can be theoretically 100 percent. It is therefore considered that the volume phase type hologram can be applied not only as a display hologram for recording images but also as a variety of optical devices utilizing high diffraction efficiency, such as a grating device, an optical division device, an optical coupling device and a laser beam scanning device.
The volume phase hologram of a reflection type in particular has intense interference activity and remarkable wavelength selectivity and can hence permit reconstruction in white light. Therefore, the volume phase hologram of a reflection type due to this feature and brightness of its reconstructed image is attracting wide attention. Further, due to its high wavelength selectivity, it is put to practical use in some areas such as head-up displays for an aircraft, an automobile and a vehicle and laser protection ophthalmic glasses.
The material for the volume phase type hologram has been selected from photosensitive materials for photograph typified by a silver halide emulsion and dichromated gelatin (DCG). The silver halide emulsion and DCG have so far been widely used since the former has high sensitivity and the latter has excellent optical properties such as high diffraction efficiency.
Since, however, DCG is poor in storage stability, it is always required to prepare DCG before exposure. Further, it requires complicated wet processing such as development and fixing after holographic exposure, and it also has a problem in that a hologram produced therefrom is still insufficient in light resistance and humidity resistance. These problems hinder commercial production of a hologram from DCG.
Silver halide emulsion has sufficient performance as a holographic material as far as its sensitivity is concerned. However, the problem thereof is that it exhibits no high resolution due to its particulate properties, that is, it is not properly used for recording interference fringes having a high spatial frequency, and that the transmittance decreases. Further, there is another problem in that it is poor in light resistance when bleached for producing a phase type hologram. Moreover, it also requires important and essential but complicated wet processing such as development and fixing after holographic exposure as DCG does.
For overcoming the above problems of conventional materials for the volume phase hologram, the development of a photopolymer is under way in recent years. A photopolymer is excellent in storage stability and is essentially free of a resolution problem since it has no particulate properties. Further, it is said that it is possible to improve light resistance and humidity resistance by selecting its composition, and the problem in reconstruction of recorded data is being solved.
The photopolymer is classified into a photocrosslinkable polymer and a photopolymerizable polymer. The photocrosslinkable polymer includes a polymer whose molecule has a photocrosslinking functional group as disclosed in Japanese Laid-open Pat. Publications Nos. 114029/1983 and 211181/1983. When this polymer is used, the photocrosslinking proceeds according to light intensity distribution of interference fringes, and interference fringes are recorded as a crosslinkage distribution. In this method, therefore, development as a post step is required for obtaining high diffraction efficiency.
Concerning the photopolymerizable polymer, there is a method using a combination of a so-called photopolymerizable monomer and a binder polymer as is disclosed in U.S. Pat. Nos. 4,173,474, 4,535,041, 4,942,112 and 4,963,471 and EP 324,482. In this method, the photopolymerizable monomer is contained in an optical data-recording material, and the polymerization of the photopolymerizable monomer selectively proceeds according to light intensity distribution formed by holographic exposure, thereby to record the interference fringes. In particular, U.S. Pat. No. 4,963,471 uses a fluorine-containing polymer having a low refractive index as a binder in combination with a monomer having a high refractive index for obtaining high diffraction efficiency in a reflection type phase hologram.
On the other hand, for using volume phase holograms of either a transmission type or a reflection type in a wider fields, it is desired to impart not only excellent optical characteristics and easiness in a post step such as freedom of wet processing, but also high heat resistance and environment resistance. For achieving this object, it is expected to develop a novel material for recording a hologram, which is basically different from any prior materials.
It is an object of the present invention to provide an optical recording film which can be a hologram excellent in diffraction efficiency, resolution and transmittance.
It is another object of the present invention to provide an optical recording film excellent in heat resistance and environment resistance.
It is another object of the present invention to provide a process for the production of an optical recording film having the above excellent physical properties.
It is another object of the present invention to provide a film for optical recording to be used in the above production process, and a process for the production thereof.
It is further another object of the present invention to provide a composition useful for producing the above film for optical recording.
According to the present invention, there is provided an optical recording film (hereinafter referred to as the first optical recording film) comprising a gel having a network structure of an inorganic substance and a polymer which is from a photopolymerizable compound (A) and present in the network structure in the gel, said gel containing an optical recording-induced difference in the network structure of the gel.
Further, there is provided a film for optical recording, which comprises a gel having a network structure of an inorganic substance, a photopolymerizable compound (A) and a photoinitiator (B), the photopolymerizable compound (A) and the photoinitiator (B) being contained in the network structure.
Further, there is provided a process for the production of an optical recording film, which comprises recording optical data by exposing the above film for optical recording to actinic radiation.
Further, there is provided a composition containing a photopolymerizable compound (A), a photoinitiator (B), a metal compound (C) which is crosslinkable by self-hydrolysis when in contact with water and the subsequent polycondensation, a good solvent (D) for the above metal compound, water (E) and a catalyst (F) for the hydrolysis of the above metal compound.
Further, there is provided a process for the production of a film for optical recording, which comprises applying the above composition to a substrate and drying the composition to form a solid-like film containing a gel having a network structure of an inorganic substance, a photopolymerizable compound (A) and a photoinitiator (B), the photopolymerizable compound (A) and the photoinitiator (B) being contained in the network structure of the gel.
Further, there is provided an optical recording film (hereinafter referred to as the second optical recording film) consisting essentially of a porous gel having a network structure of an inorganic substance, said porous gel containing optical recording-induced porosity differences in the network structure.
Further, there is provided an optical recording film (hereinafter referred to as the third optical recording film) consisting essentially of a porous gel having a network structure of an inorganic substance or a gel obtained by densification of the porous gel, the porous gel or the densified gel having a optical recording-induced concavo-convex form on the surface thereof.
Further, there is provided a process for the production of an optical recording film, which comprises applying the above composition to a substrate to form a coating, drying the coating to form a film for optical recording, irradiating the film with actinic radiation to record optical data, and removing the organic component contained in the film.
The above objects are achieved by these inventions.